Liver

Blood from the intestines, rich in nutrients from digested food, flows to the liver. The liver is in the upper right of the abdomen, with most of it's bulk behind the lower right ribs. The reddish-brown, smooth-surfaced, wedge-shape liver has more than two hundred different task, mainly to do with metabolism (body chemistry). It breaks down some nutrients, builds up others, stores some until needed, and releases others when their levels in the blood fall to low.

The small intestines

The small intestines is the longest part of the digestive tract. It is 6 meters long but also the narrowest at 4 centimeters wide. It is looped, folded, and coiled into the lower part of the of the main body, the abdomen, and consist of 3 parts. First is the duodenum, about 25 centimeters long, which joins at the upper end to the stomach. It leads to the middle section, the jejunum which is 200 centimeters long. Third is the ileum which is 350 centimeters long. The ileum leads into the large intestine, in the lower right of the abdomen.

Similar as the lining of the stomach, the small intestine lining makes powerful enzyme-containing juices to break food into ever-smaller pieces. It also receives digestive juices from the pancreas and the liver, which also help the breakdown.

The small intestines is made up of many layers. The outer layer is called the serosa. The next 2 layers are muscles. The inner-most layer are villi.

The small intestine's inner-most lining is rippled into folds called plicae. These have thousand of tiny finger-like projections called villi. Each villus is about one millimeter long, and each has thousands os even tinier finger-like microvilli. The plicae, villi and microvilli give the small intestines a huge surface, bigger than the area of 5 single beds, to take in or absorb the greatest amount of digested nutrients from food.

The large intestine, appendix and rectum

After the food leaves the small intestine or small bowel, comes the large intestine or large bowel, also called the colon. It is wide, about 6 to 7 centimeters across, but shorter than the small intestine, at about 150 centimeters. It passes up the right side of the abdomen, across below the liver and stomach, down the left side, and then curves in an S shape to the lower abdomen.

The large intestine contains microbes known as gut bacteria. These gut bacteria break down certain kinds of food, especially plant foods, so the body can absorb the nutrients. The large intestine also absorbs much of the water from the leftover digested food, turning it into squishy brown lumps called faeces or bowel motions.

The appendix is a small part of the digestive tract, about the size of a little finger. It is the junction of the small and large intestines, in the lower right of the abdomen. The appendix is hollow inside and links to the main digestive tract, but does not lead anywhere else. It does not seem to have an important role.

At the end of the large intestine, the leftover and undigested contents called faeces pass into the last part of the main tract. This is the rectum which is about 15 centimeters long. The faeces stay here until it is convenient to remove them from the body. This is done by squeezing the muscles of the abdomen, to push the faeces through the loosened ring of muscle at the end of the tract, called the anus.

Stomach

After the food travels down the oesophagus(gullet), it goes into the stomach. The stomach continues to break down the food both physically and chemically.

Foods usually stay in the stomach, to get digested, for at least one hour. If the meal contained lots of fatty foods, the stay is usually longer as fats takes longer to break apart.

The stomach walls contains three layers of muscles. These muscles squirm and churn the food to turn it into a mushy soup called chyme.

The glands in the stomach lining contains parietal cells which make a powerful hydrochloric acid that kills the germs in unwisely taken contaminated food.

The hydrochloric acid, along with protein-splitting enzyme pepsin made by other cells in the stomach lining prevents the stomach from digesting itself. If there is too much acid or the mucous coat is deficient, the acidic contents of the food will erode raw spots in the stomach wall. These are called gastric ulcers.

Gastritis

Inflammation of the stomach. Caused by stress, fungi, alkalis, poisons and corrosives. To cure, one should take more vitamin A and E which is found in seeds, nuts, corn and fish.

Gullet

At the bottom of the throat (pharynx), there are two openings. One leads to the windpipe (trachea), and the other leads to the gullet (oesophagus). When you swallow food, muscles in the throat and neck raise the top of your windpipe and lower a flap called the epiglottis. These two actions close the windpipe to prevent food from entering the wrong pipe.

Upon entering the gullet, the food does not 'fall' into the stomach, instead, the food is pushed along a track by a wave like motion called peristalsis

Mouth

The mouth is the start of the digestive system. The few parts in the mouth are teeth, saliva, and the tongue.

Teeth

The human body has 2 sets of teeth. The first set of 20 teeth grows from about birth to 3 years of age. These are called baby or milk teeth. At about 6 years of age, the first set of teeth begin to drop naturally as they are replaced by a second set called adult or permanent teeth. Most people have 32 adult teeth. There are 4 different types of teeth.

•  Your front teeth are called the incisors. They bite off large food items. 
  
• Behind them are canines. These teeth are used to tear up though food. The canines are taller and more pointed compared to the incisors.
• Next in line is the pre-molars which are used for squashing and crushing food. The pre-molars are wider than both the incisors and the canines.
• At the rear of the mouth are the molars. They are used for chewing. The molars are the broadest teeth.
  

Saliva

Saliva contains a type of enzyme called amylase. This enzyme breaks apart starch. This is why when we chew starchy foods like bread, potatoes, pasta or rice, we can sometimes taste them becoming sweeter.

Tongue

The tongue taste food so that we know what we are eating. It can tell us when a food is rotten when it taste bitter. The tongue also shifts bits of food stuck among the teeth.

After the food is chewed into soft paste by the teeth, it is swallowed and continues on its digestive journey.